X-T flexure piezoelectric device

ABSTRACT

An elongated piezoelectric bar, having only one of its axes rotated relative to the crystallographic axes of the piezoelectric material, with electrodes fixedly positioned on each of four opposed major surfaces thereof to produce flexure of the bar in a plane through the length and width of the bar. The bar is constructed with the width or frequency dependent transverse dimension greater than the thickness of frequency independent transverse dimension.

United States Patent [191 Schoenfelder 1 1 X-T FLEXURE PIEZOELECTRIC DEVICE [75] Inventor: George A. Schoenfelder, Naperville,

[73] Assignee: Motorola, Inc., Chicago, Ill.

[22] Filed: Jan. 16, 1974 [21] Appl[ No.: 433,640

[52] US. Cl 310/95; 310/9.l [51] Int. Cl .1 H04r 17/00 [58] Field of Search 310/95, 8, 9.1, 9.4

[56] References Cited UNITED STATES PATENTS 3,376,439 4/1968 Vasin et a1 310/95 3,581,126 5/1971 Omlin 310/9.1

3,588,554 6/1971 Pozdnyakov 310/95 3,754,153 8/1973 Carpenter et a1 310/91 OTHER PUBLICATIONS The Marconi Review, No. 1 1 1, Vol. XVl, 4th Quarter [451 May 20, 1975 1953, Flexure Mode Quartz Oscillators," by Beane 8; Richards, pp. 141-167.

1944, of the lRE, Vol, 32, No. 4, April, 1944. Low Frequency Quartz-Crystal cuts Having Low Temperature Coefficients," Mason & Sykes, pp. 208 215.

Primary Examiner-Mark O. Budd Attorney, Agent, or FirmEugene A. Parsons; Vincent J. Rauner ABSTRACT An elongated piezoelectric bar, having only one of its axes rotated relative to the crystallographic axes of the piezoelectric material, with electrodes fixedly positioned on each of four opposed major surfaces thereof to produce flexure of the bar in a plane through the length and width of the bar. The bar is constructed with the width or frequency dependent transverse dimension greater than the thickness of frequency independent transverse dimension.

6 Claims, 3 Drawing Figures X-T FLEXURE PIEZOELECTRIC DEVICE BACKGROUND OF THE INVENTION l. Field of the Invention Elongated piezoelectric bar type crystals, operative in a flexural mode, are utilized in many low frequency devices and mainly as the time base for the electrical quartz watch. Since the crystal is utilized in timing devices and especially watches, it is essential that it be constructed as small and as rugged as possible. Further, cost is a major factor.

2. Description of the Prior Art Typical piezoelectric bar type crystals operating in the X-Y flexural modes are constructed with the thickness greater than the width in prior art structures to provide the desired frequency stability. Examples of these prior art type crystals are illustrated and described in US. Pat. No. 3,566,164, entitled, System for Resiliently Supporting an Oscillation Quartz in a Casing", and U.S. Pat. No. 3,58l,126, entitled, Mounting Device for Flexion Vibrators.

N-T cut crystals are utilized in prior art devices as the time base, which crystals are the bar type with the thickness being less than the width. However, N-T cut crystals are extremely complicated to cut, since the axes of the bar are rotated about two (X and Y) crystal lographic axes of the piezoelectric material a specific amount. Further, these crystals must be relatively wide to provide two major opposed surfaces, each carrying a pair of electrodes for activating the crystal in the flexural mode. Also, this crystal must be relatively long to provide the desired frequency.

SUMMARY OF THE INVENTION The present invention pertains to an improved piezoelectric, bar type crystal operative in a flexural mode wherein the bar is cut so that only one axis thereof is rotated about a crystallographic axis and the width is greater than the thickness, said bar having four major side surfaces with an electrode fixedly positioned on each of said four major surfaces.

It is an object of the present invention to provide an improved piezoelectric, bar type crystal operative in a flexural mode.

It is a further object of the present invention to provide an improved piezoelectric, bar type crystal having a thickness less than the width which is more economi cal, because it uses less piezoelectric material, has improved shock resistance, because of the lower mass, and has a lower resistance and CJC, ratio for improved electrical characteristics.

These and other objects of this invention will become apparent to those skilled in the art upon consideration of the accompanying specification, claims and drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS Referring to the drawings, wherein like characters indicate like parts throughout the figures:

FIG. 1 is a view in perspective illustrating the orientation of the piezoelectric quartz bar relative to the crystallographic axes of the material;

FIG. 2 is a view in side ilevation of the improved X-T flexure quartz crystal affixed to a mounting base; and

FIG. 3 is an end view of the quartz bar illustrated in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, a blank 10 is illustrated having a width W, a thickness T and a length L. The blank 10 is formed of piezoelectric material which in the present embodiment is quartz, but it should be understood by those skilled in the art that other piezoelectric material might be used. Typical values for the length, width and thickness are L 0.442 inches, W 0.029 inches and T 0.0l6 inches. The quartz blank 10 has a generally rectangularly shaped cross section with a first transverse axis extending generally in the direction of the width, a second transverse axis extending generally in the direction of the thickness and the longitudinal axis extending in the direction of the length. The first and second transverse axes and the longitudinal axis of the blank 10 are simply the physical axes of the blank 10 and are not specifically illustrated. The crystallographic axes X, Y and Z, which correspond to the main directions ofa crystal lattice as is well known in crystallography, of the quartz material forming the quartz blank 10 are illustrated in FIG. I. In the embodiment illustrated, the physical axes of the quartz blank 10 are rotated, relative to the crystallographic axes, approximately 5 about the X crystallographic axis. In this particular cut, which will be referred to as an X-T cut (an X-Y cut has a single rotation about the X axis and, as will be seen presently, the present blank operates similar to an N-T cut so that the term X-T cut has been coined to describe the crystal) the crystal blank I0 is rotated only about the X crystallographic axis and is substantially unrotated about the Y and Z crystallographic axes, In the illustrated embodiment, the blank 10 is rotated approximately 5 about the X crystallographic axis but it should be understood that in other embodiments the physical axes of the blank may be rotated within a range of approximately il5 (including 0) and it may be possible to rotate the physical axes about a crystallographic axis other than the X axis. Since the physical axes of the blank 10 are only rotated about the X axis the blank 10 is much easier to cut, whereby the cost and number of rejects are substantially reduced compared to an N-T crystal.

Referring to FIGS. 2 and 3, the quartz blank 10 is illustrated with electrodes II, 12, 13 and 14 each affixed to one of the four major surfaces thereof, by some means such as plating or the like, which means are well known to those skilled in the art. Electrodes 11 and 13 are interconnected and electrodes 12 and 14 are interconnected, by plated connections or the like not shown in detail but well understood by those skilled in the art, so that electrodes Il-l3 have the same charge thereon and electrodes l2l4 have the same charge thereonv Mounting and connecting lead 16 is affixed to opposed electrodes 12 and I4 and lead 17 is affixed to opposed electrodes 11 and 13 (by connections on the surfaces of blank 10 which are not shown in detail) to provide physical mounting of the blank 10 and electrical connections to the electrodes 11 through I4. The other ends of the leads l6 and 17 are afiixed to ends of pins 18 and I9, respectively. which pins extend through a base 20. The base 20 is adapted to receive a housing (not shown) in engagement therewith so as to completely enclose the blank 10 for the protection thereof.

When an alternating voltage is applied across the leads 16 and 17, opposed electrodes 12-14 and 11-13 3 have opposite charges thereon which cause a fle ting oi the quartz blank 10 as illustrated in dotted lines in Fifi 2. The flexing of the quartz blank 10 occurs in a plane through the first transverse axis. or the width. and the longitudinal axis. or the length. of the blank 10. As illustrated in FIG. 2, the leads l6 and 17 are affixed to the electrodes 12 and 14 at nodal points of the quartz blank 10. Nodal points are points at which little or no movement (except possibly some torsional movementl occurs. as illustrated in FIG. 2. In the embodiment illus trated, the blank 10 has two nodal points. one adjacent each end thereof. but it should be understood that this is strictly for illustrative purposes and blanks may be constructed with more or less nodal points. if desired It has been found that the resonant frequency of the quartz blank 10 described in this application is dependent upon the width and length of the quartz blank 10 as described in the formula where F is the resonant frequency in cycles per second of the quartz blank. K is a constant, W is the width or frequency dependent transverse dimension of the quartz blank and L is the length of the quartz blank. Thus. since the thickness of the quartz blank 10 does not affect the resonant frequency thereof the thickness can be made less than the width to substantially reduce the size thereof. The volume of the quartz blank 10 is generally V4 to its the volume of an N-T cut quartz blank of the same frequency. Further. the volume of the quartz blank 10 is approximately 12 the volume of a prior art X-Y flexure quartz blank. Because of this sub' stantial reduction in volume. or mass. the present quartz crystal has a substantially improved resistance to shock. Also. because of this reduction in volume the present quartz crystal has a substantially lower resistance and lower C,,/C ratio. Many other advantages will be apparent to those skilled in the art.

While I have shown and described a specific embodiment of this invention. further modifications and improvements will occur to those skilled in the art. I desire it to be understood. therefore. that this invention is not limited to the particular form shown and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.

I claim:

1. An improved piezoelectric crystal operative in a flexural mode comprising:

a. an elongated piezoelectric bar having a generally rectangular cross section with four major side surfaces and two end surfaces;

b. said bar having first or width and second or thickness transverse axes lying generally along the X crystallographic axis or frequency dependent transverse dimension and the Z crystallographic axis or frequency independent transverse dimension. respectively. and a longitudinal axis. one of said first and sccord trans erse and saw; longitudinal ates being rotated. relati 'e to a -r -.tallgr;r hic $1 .15 cf the piezoelectric material. and the other tw c oi said first and second transverse and said longitudinal axes being substantially unrotated relatiw: to the remaining crystallographic axes.

c. said bar further having a greater width than th|ckness'.

. an electrode fixedly positioned on each of said four ma or surfaces for producing flexures of said bar in a plane through the first transverse axis and the longitudinal axis of the bar upon proper energization of said electrodes; and

e. crystal mounting and connecting means connected to said electrodes for physically mounting said crystal and providing an electrical connection to said electrodes.

2. An improved piezoelectric crystal operative in a flexural mode as claimed in claim 1 wherein the one rotated axis is rotated an amount in the range of approximately :l5.

3. An improved piezoelectric crystal operative in a flexural mode as claimed in claim I wherein the longitudinal axis is the single rotated axis.

4. An improved piezoelectric crystal operative in a flexural mode as claimed in claim 1 wherein the piezoelectric crystal is composed of quartz.

5. An improved piezoelectric crystal operative in a flexural mode comprising:

a. an elongated piezoelectric bar having a generally rectangular cross section with four major side surfaces and two end surfaces;

b. first or width and second or thickness transverse axes lying generally along the X crystallographic axis or frequency dependent transverse dimension and the Z crystallographic axis or frequency inde pendent transverse dimension, respectively. of said bar being substantially unrotated relative to the Y and Z crystallographic axes of the piezoelectric material and the longitudinal axis of said bar being rotated an amount in the range of approximately 115 about the X crystallographic axis;

. said bar further having a greater width than thick ness'.

an electrode fixedly positioned on each of said four major surfaces for producing flexures of said bar in a plane through the first transverse axis and the longitudinal axis of the bar upon proper energization of said electrodes; and

e. crystal mounting and connecting means connected to said electrodes for physically mounting said crystal and providing an electrical connection to said electrodes.

6. An improved piezoelectric crystal operative in a fiexural mode as claimed in claim 5 wherein opposed electrodes are connected together and connected pairs of electrodes are adopted to have opposed electrical charges thereon. 

1. An improved piezoelectric crystal operative in a flexural mode comprising: a. an elongated piezoelectric bar having a generally rectangular cross section with four major side surfaces and two end surfaces; b. said bar having first or width and second or thickness transverse axes lying generally along the X crystallographic axis or frequency dependent transverse dimension and the Z crystallographic axis or frequency independent transverse dimension, respectively, and a longitudinal axis, one of said first and second transverse and said longitudinal axes being rotated, relative to a crystallographic axis of the piezoelectric material, and the other two of said first and second transverse and said longitudinal axes being substantially unrotated relative to the remaining crystallographic axes; c. said bar further having a greater width than thickness; d. an electrode fixedly positioned on each of said four major surfaces for producing flexures of said bar in a plane through the first transverse axis and the longitudinal axis of the bar upon proper energization of said electrodes; and e. crystal mounting and connecting means connected to said electrodes for physically mounting said crystal and providing an electrical connection to said electrodes.
 2. An improved piezoelectric crystal operative in a flexural mode as claimed in claim 1 wherein the one rotated axis is rotAted an amount in the range of approximately + or - 15*.
 3. An improved piezoelectric crystal operative in a flexural mode as claimed in claim 1 wherein the longitudinal axis is the single rotated axis.
 4. An improved piezoelectric crystal operative in a flexural mode as claimed in claim 1 wherein the piezoelectric crystal is composed of quartz.
 5. An improved piezoelectric crystal operative in a flexural mode comprising: a. an elongated piezoelectric bar having a generally rectangular cross section with four major side surfaces and two end surfaces; b. first or width and second or thickness transverse axes lying generally along the X crystallographic axis or frequency dependent transverse dimension and the Z crystallographic axis or frequency independent transverse dimension, respectively, of said bar being substantially unrotated relative to the Y and Z crystallographic axes of the piezoelectric material and the longitudinal axis of said bar being rotated an amount in the range of approximately + or - 15* about the X crystallographic axis; c. said bar further having a greater width than thickness; d. an electrode fixedly positioned on each of said four major surfaces for producing flexures of said bar in a plane through the first transverse axis and the longitudinal axis of the bar upon proper energization of said electrodes; and e. crystal mounting and connecting means connected to said electrodes for physically mounting said crystal and providing an electrical connection to said electrodes.
 6. An improved piezoelectric crystal operative in a flexural mode as claimed in claim 5 wherein opposed electrodes are connected together and connected pairs of electrodes are adopted to have opposed electrical charges thereon. 